The present disclosure is directed toward apparatus and methods for treating joints and in particular, to treating ankle joints affected with osteoarthritis.
A joint is the location at which two or more bones make contact. Joints are constructed to allow movement and provide mechanical support, and are classified structurally and functionally. Structural classification is determined by how the bones connected to each other, while functional classification is determined by the degree of movement between the articulating bones. In practice, there is significant overlap between the two types of classifications.
There are three structural classifications of joints, namely fibrous or immovable joints, cartilaginous joints and synovial joints. In fibrous/immovable joints, bones are connected by dense connective tissue, consisting mainly of collagen. The fibrous joints are further divided into three types:                sutures which are found between bones of the skull;        syndesmosis which are found between long bones of the body; and        gomphosis which is a joint between the root of a tooth and the sockets in the maxilla or mandible.        
Cartilaginous bones are connected entirely by cartilage (also known as “synchondroses”). Cartilaginous joints allow more movement between bones than a fibrous joint but less than the highly mobile synovial joint. Cartilaginous joints include the artificial discs of the spine.
Synovial joints have a space between the articulating bones and surrounding cartilage for synovial fluid. This classification contains joints that are the most mobile of the three, and includes the hip, knee, ankle and shoulder.
Joints can also be classified functionally, by the degree of mobility they allow. Synarthrosis joints permit little or no mobility. They can be categorized by how the two bones are joined together. That is, synchrondoses are joints where the two bones are connected by a piece of cartilage. Synostoses are where two bones that are initially separated eventually fuse together as a child approaches adulthood. By contrast, amphiarthrosis joints permit slight mobility. The two bone surfaces at the joint are both covered in hyaline cartilage and joined by strands of fibrocartilage. Most amphiarthrosis joints are cartilaginous.
Diarthrosis joints permit a variety of movements (e.g. flexion, adduction, pronation). Only synovial joints are diarthrodial and they can be divided into six classes according to their motion: 1. ball and socket—such as the shoulder or the hip; 2. hinge—such as the elbow and ankle; 3. pivot—such as the radius and ulna; 4. condyloidal (or ellipsoidal)—such as the wrist between radius and carps or knee; 5. saddle—such as the thumb joint; and 6. gliding—such as between the carpals.
Synovial joints (or diarthrosis or diarthroidal joints) are the most common and most moveable type of joints in the body. As with all other joints in the body, synovial joints achieve movement at the point of contact of the articulating bones. Structural and functional differences distinguish the synovial joints from the two other types of joints in the body, with the main structural difference being the existence of a cavity between the articulating bones and the occupation of a fluid in that cavity which aids movement. The whole of a diarthrosis is contained by a ligamentous sac, the joint capsule or articular capsule. The surfaces of the two bones at the joint are covered in cartilage. The thickness of the cartilage varies with each joint, and sometimes may be of uneven thickness. Articular cartilage is multi-layered. A thin superficial layer provides a smooth surface for the two bones to slide against each other. Of all the layers, it has the highest concentration of collagen and the lowest concentration of proteoglycans, making it very resistant to shear stresses. Deeper than that is an intermediate layer, which is mechanically designed to absorb shocks and distribute the load efficiently. The deepest layer is highly calcified, and anchors the articular cartilage to the bone. In joints where the two surfaces do not fit snugly together, a meniscus or multiple folds of fibro-cartilage within the joint correct the fit, ensuring stability and the optimal distribution of load forces. The synovium is a membrane that covers all the non-cartilaginous surfaces within the joint capsule. It secretes synovial fluid into the joint, which nourishes and lubricates the articular cartilage. The synovium is separated from the capsule by a layer of cellular tissue that contains blood vessels and nerves.
Various maladies can affect the joints, one of which is arthritis. Arthritis is a group of conditions where there is damage caused to the joints of the body. Arthritis is the leading cause of disability in people over the age of 65.
There are many forms of arthritis, each of which has a different cause. Rheumatoid arthritis and psoriatic arthritis are autoimmune diseases in which the body is attacking itself. Septic arthritis is caused by joint infection. Gouty arthritis is caused by deposition of uric acid crystals in the joint that results in subsequent inflammation. The most common form of arthritis, osteoarthritis is also known as degenerative joint disease and occurs following trauma to the joint, following an infection of the joint or simply as a result of aging.
Unfortunately, all arthritides feature pain. Patterns of pain differ among the arthritides and the location. Rheumatoid arthritis is generally worse in the morning; in the early stages, patients often do not have symptoms following their morning shower.
Osteoarthritis (OA, also known as degenerative arthritis or degenerative joint disease, and sometimes referred to as “arthrosis” or “osteoarthrosis” or in more colloquial terms “wear and tear”), is a condition in which low-grade inflammation results in pain in the joints, caused by wearing of the cartilage that covers and acts as a cushion inside joints. As the bone surfaces become less well protected by cartilage, the patient experiences pain upon weight bearing, including walking and standing. Due to decreased movement because of the pain, regional muscles may atrophy, and ligaments may become more lax. OA is the most common form of arthritis.
A particular form of OA is post-traumatic osteoarthritis or PTOA. As it is understood, articular surface incongruities resulting from trauma are believed to subject a joint to elevated contact stresses which over time results in the development of PTOA in the joint. Finite element stress analysis has been employed to assess joint mechanics throughout an entire sequence of load variation encountered during gait (See “Is Elevated Contact Stress Predictive of Post-Traumatic Osteoarthritis for imprecisely Reduced Tibial Plafond Fractures?,” Anderson et al., 2010 Orthopaedic Research Society, Wiley Periodicals, Inc.). While recognizing that joint loading is intermittent and varies over a gait cycle, FE modeling techniques have enabled the computation of elevated contact stresses produced by incongruities from trauma such as a fracture. It has thus been possible to assess a relationship between elevated contact stresses and PTOA onset in joints of patients with intra-articular fractures by comparing stresses within joints suffering from trauma to stresses within intact joints.
The main symptom of osteoarthritis is chronic pain, causing loss of mobility and often stiffness. “Pain” is generally described as a sharp ache, or a burning sensation in the associated muscles and tendons. OA can cause a crackling noise (called “crepitus”) when the affected joint is moved or touched, and patients may experience muscle spasm and contractions in the tendons. Occasionally, the joints may also be filled with fluid. Humid weather increases the pain in many patients.
OA affects the hand, feet, spine, and the large weight-bearing joints, such as the hips, knees and ankles, although in theory, any joint in the body can be affected. OA may begin or progress if excess stress or weight is placed on the joint. Several conditions can lead to excess stress or weight on the joint, including anatomy, injury, or obesity. When too much stress is placed on the joint as OA progresses, the affected joint appears larger, is stiff and painful, and usually feels worse, the more the joint is used and loaded throughout the day, thus distinguishing OA from rheumatoid arthritis. With progression in OA, cartilage looses its viscoelastic properties and its ability to absorb load. Generally speaking, the process of clinical detectable osteoarthritis is irreversible, and typical treatment consists of medication or other interventions that can reduce the pain of OA and thereby improve the function of the joint. While drugs and certain cartilage repair procedures may temporarily relieve pain, they often do not treat the underlying problems that led to OA. Conversely, research suggests that if the excess stress on the joint is removed, pain may decrease, and the natural joint tissues may demonstrate some recovery.
A variety of surgical procedures have been developed with the aim of decreasing or eliminating pain and improving function in patients with advanced osteoarthritis (OA). The different approaches include preservation or restoration of articular surfaces, total joint replacement with artificial implants, osteotomy and arthrodesis (fusion).
Arthrodesis are described as being reasonable alternatives for treating OA of small hand and foot joints as well as degenerative disorders of the spine, but were deemed to be rarely indicated in large weight-bearing joints such as the hip due to functional impairment of gait, cosmetic problems and further side-effects. Arthrodesis of the ankle is used as a last resort procedure and is often successful in relieving pain, however, gait and mobility are adversely affected.
Joint replacement is one of the most common and successful operations in modern orthopaedic surgery. It consists of replacing painful, arthritic, worn or diseased parts of the joint with artificial surfaces shaped in such a way as to allow joint movement. Such procedures are a last resort treatment as they are highly invasive and require substantial periods of recovery. Joint replacement is sometimes called total joint replacement indicating that all joint surfaces are replaced. This contrasts with hemiarthroplasty (half arthroplasty) in which only one bone's joint surface is replaced and unincompartmental arthroplasty in which both surfaces of the knee, for example, are replaced but only on the inner or outer sides, not both. Thus, arthroplasty as a general term, is an operative procedure of orthopaedic surgery performed, in which the arthritic or dysfunctional joint surface is replaced. Alternatively, loading patterns and associated stresses on painful joints can be modified by realigning the joint by osteotomy or other procedures. These procedures are all characterized by relatively long recovery times and are highly invasive procedures.
Other approaches to treating osteoarthritis involve an analysis of loads which exist at a joint. Both cartilage and bone are living tissues that respond and adapt to the loads they experience. If a joint surface remains unloaded for appreciable periods of time the cartilage tends to soften and weaken. Further, as with most materials that experience structural loads, particularly cyclic structural loads, both bone and cartilage begin to show signs of failure at loads that are below their ultimate strength. However, cartilage and bone have some ability to repair themselves. Research has shown that some mechanical stimulation can enhance the healing response and it is likely that the optimum regime for a cartilage/bone graft or construct will involve different levels of load over time, e.g. during a particular treatment schedule. Thus, there is a need for devices which facilitate the control of load on a joint undergoing treatment or therapy, to thereby enable use of the joint within a healthy loading zone.
Certain other approaches to treating osteoarthritis contemplate external devices such as unloader braces or fixators which control the motion of the bones at a joint. Various of these approaches have had some success in alleviating pain but suffer from lack of patient compliance or lack an ability to facilitate and support the natural motion and function of the diseased joint.
In osteoarthritis of the ankle the cartilage that normally allows the ankle to move smoothly has broken down. When the gliding surface of the cartilage is damaged, the lower ends of the tibia and fibula grind against the top of the talus, creating pain and loss of normal ankle movement. Osteoarthritis can occur in patients due to genetic predisposition and ordinary wear and tear or can be associated with trauma. As stated, trauma related arthritis results when the joint is injured either by fracture, dislocation or damage to the ligaments surrounding the joint. This resulting damage predisposes the joint to osteoarthritis.
Treatments for ankle osteoarthritis include conservative approaches such as weight loss, physical therapy and anti-inflammatory medicine. However, clinical literature correlating and quantifying OA relief from weight loss has not been identified with respect to the ankle. In more severe cases, surgical interventions including distal tibial osteotomy, ankle replacement or fusion may be required. Ankle replacement is a form of joint replacement where the ankle joints are replaced with artificial joints made from metal alloys and lightweight plastic. Ankle fusion is the other option where the bones of the ankle joint are locked together with screws and plates. Ankle fusion and replacement procedures are characterized by relatively long recovery times and are highly invasive procedures.
There is a need for a treatment modality which bridges the gap between the more conservative approaches such as weight loss, physical therapy and anti-inflammatory medicine and a decision to seek major surgical intervention. Such a treatment modality should be minimally invasive yet sufficiently effective to reduce the pain of osteoarthritis. The treatment should also be compatible with ankle anatomy taking into consideration the tendons and muscles overlaying the ankle joint and relatively thin skin at the ankle, as well as contact stresses within the joint. In particular, consideration of measured contact stresses and a predetermined threshold can be useful in directing treatment. The treatment should not be hindering or only minimally hinder normal motion of the ankle joint.
The present disclosure addresses these and other needs.